4-Phenyl-1,2,3-thiadiazoles as herbicide extenders

ABSTRACT

Herbicidally active thiolcarbamates are employed in combination with certain 4-phenyl-1,2,3-thiadiazoles having the formula ##STR1## in which R 4  is selected from the group consisting of trifluoromethyl and ##STR2## in which R 5  is selected from the group consisting of C 1  -C 3  alkyl, phenyl, and phenyl substituted with one or more members selected from the group consisting of halogen and trifluoromethyl. In a typical application, the 4-phenyl-1,2,3-thiadiazole is included in sufficient quantity to lessen the rate of soil degradation of the thiolcarbamate. As a result, the herbicidal effectiveness of the thiolcarbamate is enhanced and prolonged, rendering a single application of the herbicide effective over a longer period of time.

This is a continuation of application Ser. No. 244,419 filed Mar. 16,1981 now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to herbicide extenders, herbicidal compositions,and herbicidal methods. In particular, this invention is addressed tothe problem of herbicidal degradation occurring in certain soils.

Thiolcarbamates are well known in the agricultural art as herbicidesuseful for weed control in crops such as corn, potatoes, beans, beets,spinach, tobacco, tomatoes, alfalfa, and rice. Thiolcarbamates areprimarily used in pre-emergence application, and are particularlyeffective when incorporated into the soil prior to the planting of thecrop. The concentration of the thiolcarbamate in the soil is greatestimmediately after application of the compound. How long thereafter theinitial concentration is retained depends in large part on theparticular soil used. The rate at which the thiolcarbamate concentrationdeclines following its application varies from one type of soil to thenext. This is evident both in the observable extent of weed control andin the detectable presence of undegraded thiolcarbamate remaining in thesoil after considerable time has elapsed.

It is therefore an object of this invention to increase the soilpersistance of thiolcarbamate herbicides and thus improve theirherbicidal effectiveness.

BRIEF DESCRIPTION OF THE INVENTION

It has now been discovered that the soil persistence of certainherbicidally active thiolcarbamates is significantly extended by thefurther addition to the soil of certain extender compounds in the formof 4-phenyl-1,2,3-thiadiazoles, which have little or no herbicidalactivity of their own and do not decrease the herbicidal activity of thethiolcarbamate. This improvement in the soil persistence ofthiolcarbamates manifests itself in a variety of ways. It can be shown,for example, by soil analyses taken at regular intervals, that the rateof decrease of the thiolcarbamate content of the soil is substantiallylessened. Improved soil persistence can also be shown by improvements inherbicidal efficacy, as evidenced by a higher degree of weed injurybrought about when the extender compound increases the soil persistenceof the thiolcarbamate, prolonging its effective life.

In particular, this invention relates to a novel herbicidal compositioncomprising

(a) an herbicidally effective amount of a thiolcarbamate having theformula ##STR3## in which R¹, R², and R³ are independently C₂ -C₄ alkyl;and

(b) an amount of a 4-phenyl-1,2,3-thiadiazole sufficient to extend thesoil life of said thiolcarbamate, said 4-phenyl-1,2,3-thiadiazole havingthe formula ##STR4## in which R⁴ is selected from the group consistingof trifluoromethyl and ##STR5## in which R⁵ is selected from the groupconsisting of C₁ -C₃ alkyl, phenyl, and phenyl substituted with one ormore members selected from the group consisting of halogen andtrifluoromethyl.

Within the scope of the present invention, certain embodiments arepreferred, namely:

In the thiolcarbamate formula, R¹ is preferably ethyl, and R² and R³ areeach preferably propyl.

In the thiadiazole formula, R⁴ is preferably selected from the groupconsisting of trifluoromethyl and ##STR6## in which R⁵ is selected fromthe group consisting of methyl, chlorophenyl, dichlorophenyl,trifluoromethylphenyl, and chlorotrifluoromethylphenyl. (The term"chlorotrifluoromethylphenyl" denotes a phenyl ring containing chlorineand trifluoromethyl as separate substituents.)

This invention further relates to a method of controlling undesirablevegetation comprising applying the above compositions to the locus wherecontrol is desired.

In addition, several of the above thiadiazoles are novel, namely thosehaving the formula ##STR7## in which R is selected from the groupconsisting of C₁ -C₃ alkyl, phenyl, and phenyl substituted with one ormore members selected from the group consisting of halogen andtrifluoromethyl.

Of these novel thiadiazoles, the preferred ones are those in which R isselected from the group consisting of methyl, chlorophenyl,dichlorophenyl, trifluoromethylphenyl, and chlorotrifluoromethylphenyl.

The term "alkyl" is used herein to include both straight-chain andbranched-chain groups. All carbon atom ranges are inclusive of theirupper and lower limits.

The term "herbicide," as used herein, means a compound or compositionwhich controls or modifies the growth of plants. By the term"herbicidally effective amount" is meant any amount of such compound orcomposition which causes a modifying effect upon the growth of plants.By "plants" is meant germinant seeds, emerging seedlings, andestablished vegetation, including roots and above-ground portions. Suchcontrolling or modifying effects include all deviations from naturaldevelopment, such as killing, retardation, defoliation, desiccation,regulation, stunting, tillering, stimulation, leaf burn, dwarfing andthe like.

The phrase "to extend the soil life of said thiolcarbamate" as usedherein means to retard the rate at which molecules of thiolcarbamate arebroken down into decomposition products when in contact with soil and/orto prolong the period of time following application in which herbicidaleffects can be observed. This applies both to field sites where repeatedapplications of thiolcarbamates result in decreasing herbicidaleffectiveness, and to field sites where a decline in herbicidal activityis detected over time regardless of the prior history of herbicidalapplications. An extended soil life can be demonstrated by a slower rateof decline of weed-killing activity, or an increased half-life ofthiolcarbamate concentration in the soil. Other techniques ofdetermining soil life are readily apparent to one skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

Thiolcarbamates within the scope of the present invention can beprepared by the process described in U.S. Pat. No. 2,913,327 (Tilles etal., Nov. 17, 1959). Examples of such thiolcarbamates include S-ethylN,N-di-n-propylthiolcarbamate, S-ethyl N,N-diisobutylthiolcarbamate,S-n-propyl N,N-di-n-propylthiolcarbamate, and S-n-propylN-ethyl-N-n-butyl-thiolcarbamate.

Thiadiazoles within the scope of this invention can be prepared byprocesses described in Lemieux et al., U.S. Pat. No. 3,464,999 (Sept. 2,1969). Generally, an appropriately substitutedcarbethoxyhydrazinoacetophenone is obtained by reacting thecorresponding acetophenone with carbethoxyhydrazine in the presence ofglacial acetic acid and a solvent such as methanol. Thecarbethoxyhydrazinoacetophenone is then reacted with thionyl chloride toproduce the 4-phenyl-1,2,3-thiadiazole. The N-alkylcarbamoyloxyphenylthiadiazoles can be produced from the hydroxyphenyl analog by reactionof the latter with an alkyl isocyanate.

The objects of the present invention are achieved by applying theextender compound to the soil at an agricultural field site inconjunction with the herbicide. The two compounds can be appliedsimultaneously in a single mixture or in separate formulations, or theycan be applied in succession, with either one following the other. Insuccessive application, it is preferable to add the compounds as closein time as possible.

The herbicide extending effect is operable over a wide range of ratiosof the two compounds. It is most convenient, however, to apply thecompounds at a ratio of about 1:1 to about 20:1 (herbicide:extender) ona weight basis, preferably about 1:1 to about 5:1, and most preferablyabout 1:1 to about 2:1.

The variety of crops on which the present composition is useful can besignificantly broadened by the use of an antidote to protect the cropfrom injury and render the composition more selective against weeds.

For antidote descriptions and methods of use, reference is made to U.S.Pat. No. 3,959,304, issued to E. G. Teach on May 25, 1976; U.S. Pat. No.3,989,503, issued to F. M. Pallos et al. on Nov. 2, 1976; U.S. Pat. No.4,021,224, issued to F. M. Pallos et al. on May 3, 1977; U.S. Pat. No.3,131,509, issued to O. L. Hoffman on May 5, 1964; and U.S. Pat. No.3,564,768, issued to O. L. Hoffman on Feb. 3, 1971.

Examples of useful antidotes include acetamides such asN,N-diallyl-2,2-dichloroacetamide and N,N-diallyl-2-chloroacetamide,oxazolidines such as 2,2,5-trimethyl-N-dichloroacetyl oxazolidine and2,2-spirocyclohexyl-N-dichloroacetyl oxazolidine, and 1,8-naphthalicanhydride. For maximum effect, the antidote is present in thecomposition in a non-phytotoxic, antidotally effective amount. By"non-phytotoxic" is meant an amount which causes at most minor injury tothe crop. By "antidotally effective" is meant an amount whichsubstantially decreases the extent of injury caused by the herbicide tothe crop. The preferred weight ratio of herbicide to antidote is about3:1 to about 20:1.

The first three examples which follow are offered to illustrate thepreparation of the novel compounds of this invention. The activity ofthese compounds together with others falling within the broader scope ofthis invention is demonstrated in Examples 4 and 5.

EXAMPLE 1 4-(4'-N-Methylcarbamoyloxyphenyl)-1,2,3-thiadiazole

A reaction vessel was charged with 2.5 g (0.014 mole) of4-(4'-hydroxyphenyl)-1,2,3-thiadiazole, 10 ml of methyl isocyanate, 5 mlof acetone, and 0.5 ml of triethylamine. The reactants were heated underreflux for one hour, then stripped in vacuo. The residue was poured intoice water and the solid product was collected by filtration and dried toyield 2.1 g of a solid with a melting point range of 156°-160° C. Themolecular structure was confirmed by mass spectrometry as that of thetitle compound.

EXAMPLE 24-[2'-N-(3"-Trifluoromethylphenyl)carbamoyloxyphenyl]-1,2,3-thiadiazole

A reaction vessel was charged with 1.8 g (0.01 mole) of4-(2'-hydroxyphenyl)-1,2,3-thiadiazole, 1.8 g (0.01 mole) of3-trifluoromethylphenylisocyanate, 5 ml of methylene chloride, and threedrops of triethylamine. The temperature of the mixture rose to 30° C.and the mixture was allowed to stand for one hour at ambient conditions.The mixture was then stripped in vacuo to yield 3.6 g of a glassymaterial (highly viscous liquid), whose molecular structure wasconfirmed by mass spectrometry as that of the title compound.

EXAMPLE 34-[2'-(3",4"-Dichlorophenylcarbamoyloxy)phenyl]-1,2,3-thiadiazole

A reaction vessel was charged with 1.8 g (0.01 mole) of4-(2'-hydroxyphenyl)-1,2,3-thiadiazole, 1.9 g (0.01 mole) of3,4-dichlorophenylisocyanate, 25 ml of methylene chloride, and threedrops of triethylamine. The temperature of the mixture rose to 35° C.After the exotherm subsided, the solvent was removed in vacuo to yield3.5 g of a glassy material (highly viscous liquid), whose molecularstructure was confirmed by mass spectrometry as that of the titlecompound.

EXAMPLE 4

This example shows, by soil analysis, the effectiveness of thethiadiazoles of the present invention in extending the soil life ofthiolcarbamates. The thiolcarbamate used in this test was S-ethylN,N-di-n-propylthiolcarbamate, commonly known as EPTC. The soil was asandy loam soil obtained from Sunol, Calif., containing approximately(on a weight basis) 64% sand, 29% silt, and 7% clay, determined bymechanical means. The total organic content of the soil wasapproximately 4% by weight and the pH was 6.8, both determined bychemical analysis.

The test procedure involved an initial pre-treatment of the soil tosimulate field conditions where the soil had been previously treatedwith EPTC, followed by a soil persistence test, as described below.

A. Soil Pre-Treatment

An emulsion was prepared by diluting an emulsifiable liquid concentratecontaining 6 lb/gal (0.72 kg/l) of the thiolcarbamate in 100 ml ofwater, such that the concentration of thiolcarbamate in the resultingemulsion was 4000 mg/l. Five ml of this emulsion was then added to 10 lb(4.54 kg) of soil and the mixture was mixed in a rotary mixer for 10-20seconds.

Round plastic containers, 9 inches (22.9 cm) in diameter by 9 inches(22.9 cm) deep, were then filled with the sandy loam soil, which wastamped and leveled with a row marker to impress three rows across thewidth of each container. Two rows were seeded with DeKalb XL-45A cornZea mays (L.), and one row was seeded with barnyardgrass Echinochloacrusgalli (L.). Sufficient seeds were planted to produce severalseedlings per row. The containers were then placed in a greenhousemaintained at 20° C. to 30° C. and watered daily by sprinkler.

Five weeks after treatment, the soil was allowed to dry out and theplant foliage was removed. The soil was then passed through a 0.25 inch(0.64 cm) screen, followed by a 2-millimeter (mm) screen, to removeplant roots and clods.

B. Soil Persistence Test

A 100-gram quantity (air-dry basis) of the pre-treated soil was placedin an 8-ounce (0.25 liter) wide-mouth glass bottle. The sameemulsifiable concentrate described in Part A above was appropriatelydiluted in water such that a 5-ml portion added to the soil wouldproduce a herbicide concentration of 6 ppm (weight) in the soil. This isequivalent to an application rate of 6 pounds per acre (6.7 kilograms)per hectare) in a field where the herbicide is incorporated into thesoil through a depth of about 2 inches (5.08 cm) soon after application.A selected extender compound in technical (nonformulated) form was thendiluted in an acetone-water mixture such that a one-ml portion added tothe soil would produce a concentration of 4 ppm by weight, equivalent to4 pounds per acre (4.5 kilograms per hectare). On these bases, theherbicide and extender were added to the bottle containing the soil. Thebottle was then sealed with a lid and shaken manually for approximately15 minutes.

Following such treatment, the soil was moistened with 20 ml of deionizedwater. The bottle was then covered with a watch glass to maintainaerobic conditions and to prevent rapid soil drying, and placed in acontrolled environmental chamber in darkness, where the temperature wasmaintained constant at 25° C.

Four days later, the bottle was removed from the environmental chamberand 25 ml of water and 100 ml of toluene were added. The bottle was thentightly sealed with a lid containing a cellophane liner, and vigorouslyshaken on a variable speed, reciprocating shaker (Eberbach Corp. Model6000) set at approximately 200 excursions per minute for one hour. Aftershaking, the bottle contents were allowed to settle, and a 10 ml aliquotof toluene was transferred by pipette into a glass vial and sealed witha polyseal cap. The toluene extract was analyzed for herbicidal contentby gas chromatography. The chromatogram data was then converted toequivalent soil concentrations in parts per million (ppm) by weight ofthe herbicide.

The results are shown in the table below, where the eight compounds weretested in three separately treated batches of soil. A control runwithout an extender compound was conducted for each soil batch, to showhow the drop in herbicide concentration was affected by the extendercompound. In each case, the quantity of herbicide remaining in the soilafter four days was dramatically increased when the extender compoundwas added.

                  TABLE I                                                         ______________________________________                                        4-DAY SOIL PERSISTENCE DATA                                                   Herbicide:                                                                            SEthyl N,Ndi-n-propylthiolcarbamate                                           (EPTC) at 6 lb/A (6 ppm in soil)                                      Extender:                                                                             As shown at 4 lb/A (4 ppm in soil)                                                            EPTC                                                                          Residue After                                                                 4 Days (ppm)                                          Extender                      With                                            Com-                          Ex-    Without                                  pound                         tend-  Ex-                                      No.    Structural Formula     er     tender                                   ______________________________________                                        Soil                                                                          Batch                                                                         1                                                                                     ##STR8##              2.00   0.33                                     2                                                                                     ##STR9##              0.51   0.33                                     Soil                                                                          Batch                                                                         B:                                                                            3                                                                                     ##STR10##             1.99   0.03                                     4                                                                                     ##STR11##             2.48   0.03                                     5                                                                                     ##STR12##             1.58   0.03                                     6                                                                                     ##STR13##             2.79   0.03                                     7                                                                                     ##STR14##             2.37   0.03                                     Soil                                                                          Batch                                                                         C:                                                                            8                                                                                     ##STR15##             1.17   0.04                                     ______________________________________                                    

EXAMPLE 5 Herbicidal Activity Improvement Tests

This example offers herbicidal activity test data to show theeffectiveness of the extender compounds in improving the herbicidalactivity of thiolcarbamates. The effect is observed by comparing theextent of weed control in test flats treated with a thiolcarbamateagainst that occurring in similar flats treated with both thethiolcarbamate and the extender.

As in Example 4, the thiolcarbamate used in this test was S-ethylN,N-di-n-propylthiolcarbamate applied in the form of an emulsifiableliquid concentrate containing 6 lb/gal (0.72 kg/l) active ingredient.The extender compounds were used in technical form. These materials wereadded to a mixture of equal parts of acetone and water at such amountsthat 5 cc of the resulting mixture when added to three pounds of soilyielded a quantity in the soil equivalent to the desired applicationrate expressed in pounds per acre. Thus, 5 cc of the mixture and threepounds of sandy loam soil from Keeton, Calif., containing approximately10.8% sand, 24.8% silt, and 4.4% clay (by weight), with an organiccontent of 0.9% by weight and a pH of 7.2, were placed in a rotarymixer. Also added was 17-17-17 fertilizer (N-P₂ O₅ -K₂ O on a weightbasis) at a quantity amounting to 50 ppm by weight with respect to thesoil.

The treated soil was then placed in aluminum flats which were 2.5 inchesdeep, 3.5 inches wide, and 7.5 inches long (6.4×8.9×19.0 cm). The soilwas tamped and leveled with a row marker to impress six rows across thewidth of the flat. The test weeds were as follows:

    ______________________________________                                        Common Name    Scientific Name                                                ______________________________________                                        green foxtail  Setaria viridis (L.) Beauv.                                    barnyardgrass  Echinochloa crusgalli (L.) Beauv.                              sorghum        Sorghum bicolor (L.) Moench                                    wild oats      Avena fatua L.                                                 shattercane    Sorghum bicolor (L.) Moench                                                   (variant of sorghum)                                           ______________________________________                                    

DeKalb XL-45A corn of species Zea mays (L.) was also planted.

Sufficient seeds were planted to produce several seedlings per inch ineach row. The flats were then placed in a greenhouse maintained at 70°to 85° F. and watered daily by sprinkler.

Three weeks after treatment, the degree of weed control and corn injurywere estimated and recorded as percentage control compared to the growthof the same species in an untreated check flat of the same age. Therating scale ranges from 0 to 100%, where 0 equals no effect with plantgrowth equal to the untreated control, and 100 equals complete kill.

Table II lists the results of these tests. Control experiments areincluded for comparison. Substantial improvements in average percentweed control over the control experiments are evident and the herbicidalefficacy of the thiolcarbamate three weeks after application was muchimproved by the use of the extender.

                  TABLE II                                                        ______________________________________                                        HERBICIDAL ACTIVITY DATA                                                      Herbicide: S--Ethyl N,N--di-n-propylthiolcarbamate                            (EPTC) at 3 lb/A                                                              Extender: As shown                                                            Evaluation Time: 3 weeks after treatment                                      Extender                                                                      Compound   Extender      % Plant Injury                                       No. (see Table I)                                                                        Application Rate                                                                            Weed Average.sup.(1)                                                                       Corn                                    ______________________________________                                        Control Data             9.25.sup.(2) 0                                       (no extender)                                                                 Test Data                                                                     1             2.0 lb/A   29           0                                       1          4.0           47           0                                       2          2.0           18           0                                       2          4.0           12           0                                       3          2.0           26           0                                       3          4.0           21           0                                       4          2.0           0            0                                       4          4.0           5            0                                       5          2.0           10           0                                       5          4.0           11           0                                       6          2.0           13           0                                       6          4.0           17           0                                       7          2.0           15           0                                       7          4.0           13           0                                       8          2.0           81           0                                       8          4.0           90           0                                       ______________________________________                                         Notes:                                                                        .sup.(1) Average of injury to five weed species (green foxtail,               barnyardgrass, sorghum, wild oats, shattercane).                              .sup.(2) Figure for control data represents overall average of four           replications.                                                            

METHODS OF APPLICATION

The herbicidal compositions of the present invention are useful incontrolling the growth of undesirable vegetation by preemergence orpost-emergence application to the locus where control is desired,including pre-plant and post-plant soil incorporation as well as surfaceapplication. The compositions are generally embodied in formulationssuitable for convenient application, containing additional ingredientsor diluent carriers to aid in the dispersal of the compositions.Examples of such ingredients or carriers are water, organic solvents,dusts, granules, surface active agents, water-oil emulsions, wettingagents, dispersing agents, and emulsifying agents. The formulatedcompositions generally take the form of dusts, emulsifiableconcentrates, granules, or microcapsules.

A. DUSTS

Dusts are dense powder compositions which combine the active compoundswith a dense, free-flowing solid carrier. They are intended forapplication in dry form and are designed to settle rapidly to avoidbeing windborne to areas where their presence is not desired.

The carrier may be of mineral or vegetable origin, and is preferably anorganic or inorganic powder of high bulk density, low surface area, andlow liquid absorptivity. Suitable carriers include micaceous talcs,pyrophyllite, dense kaolin clays, tobacco dust, and ground calciumphosphate rock.

The performance of a dust is sometimes aided by the inclusion of aliquid or solid wetting agent, of ionic, anionic, or nonionic character.Preferred wetting agents include alkylbenzene and alkylnaphthalenesulfonates, sulfated fatty alcohols, amines or acid amides, long chainacid esters of sodium isothionate, esters of sodium sulfosuccinate,sulfated or sulfonated fatty acid esters, petroleum sulfonates,sulfonated vegetable oils, and ditertiary acetylenic glycols.Dispersants are also useful in the some dust compositions. Typicaldispersants include methyl cellulose, polyvinyl alcohol, ligninsulfonates, polymeric alkylnaphthalene sulfonates, sodium naphthalenesulfonate, polymethylene bisnaphthalenesulfonate, andsodium-N-methyl-N-(long chain acid)taurates.

In addition, inert absorptive grinding aids are frequently included indust compositions to aid in the manufacturing of the dust. Suitablegrinding aids include attapulgite clay, diatomaceous silica, syntheticfine silica and synthetic calcium and magnesium silicates.

In typical dust compostiions, carriers are usually present inconcentrations of from about 30 to 90 weight percent of the totalcomposition. The grinding aid usually constitutes about 5 to 50 weightpercent, and the wetting agent up to about 1.0 weight percent.Dispersants, when present, constitutes up to about 0.5 weight percent,and minor amounts of anticaking and antistatic agents may also bepresent. The particle size of the entire composition is usually about 30to 50 microns.

B. EMULSIFIABLE CONCENTRATES

Emulsifiable concentrates are solutions in which the active materialsand an emulsifying agent are dissolved in a nonwatermiscible solvent.Prior to use, the concentrate is diluted with water to form a suspendedemulsion of solvent droplets.

Typical solvents for use in emulsifiable concentrates include weed oils,chlorinated hydrocarbons, and nonwater-miscible ethers, esters, andketones.

Typical emulsifying agents are anionic or nonionic surfactants, ormixtures of the two. Examples include long-chain mercaptan polyethoxyalcohols, alkylaryl polyethoxy alcohols, sorbitan fatty acid esters,polyoxyethylene ethers with sorbitan fatty acid esters, polyoxyethyleneglycol esters with fatty or rosin acids, fatty alkylol amidecondensates, calcium and amine salts of fatty alcohol sulfates, oilsoluble petroleum sulfonates, or preferably mixtures of theseemulsifying agents. Such emulsifying agents usually comprise about 1 to10 weight percent of the total composition.

Typical emulsifiable concentrates contain about 15 to 50 weight percentactive material, about 40 to 82 weight percent solvent, and about 1 to10 weight percent emulsifier. Other additives such as spreading agentsand stickers can also be included.

C. GRANULES

Granules are physically stable, particulate compositions in which theactive ingredients adhere to or are distributed throughout a basicmatrix of a coherent, inert carrier with macroscopic dimensions. Atypical particle is about 1 to 2 millimeters in diameter. Surfactantsare often present to aid in the leaching of the active ingredient fromthe granule to the surrounding medium.

The carrier is preferably of mineral origin, and generally falls withinone of two types. The first are porous, absorptive, preformed granules,such as attapulgite or heat expanded vermiculite. A solution of theactive agent is sprayed on the granule at concentrations of up to 25weight percent of the total weight. The second are powdered materials towhich the active ingredients are added prior to being formed intogranules. These materials include kaolin clays, hydrated attapulgite, orbentonite clays in the form of sodium, calcium, or magnesium bentonites.Water-soluble salts may also be present to help the granulesdisintegrate in water. These ingredients are blended with the activecomponents, then granulated or pelleted, followed by drying. In theresulting composition, the active component is distributed uniformlythroughout the mass. Granules can be made with as much as 25 to 30weight percent active component, but more frequently a concentration ofabout 10 weight percent is desired for optimum distribution. Granulecompositions are most useful in a size range of 15-30 mesh.

The surfactant is generally a common wetting agent of anionic ornonionic character. The most suitable wetting agents depend upon thetype of granule used. When preformed granules are sprayed with activematerial in liquid form, the most suitable wetting agents are nonionic,liquid wetters miscible with the solvent. These are compounds generallyknown as emulsifiers, and comprise alkylaryl polyether alcohols, alkylpolyether alcohols, polyoxyethylene sorbitan fatty acid esters,polyethylene glycol esters with fatty or rosin acids, fatty alkylolamide condensates, oil solution petroleum or vegetable oil sulfonates,or mixtures of these. Such agents usually comprise up to about 5 weightpercent of the total composition.

When the active ingredient is first mixed with a powdered carrier andsubsequently granulated, liquid nonionic wetters can still be used, butit is usually preferable to incorporate at the mixing stage a solid,powdered anionic wetting agent comprising up to about 2.0 weight percentof the total composition.

Typical granules comprise about 5 to 30 percent by weight activematerial, about 0 to 5 weight percent wetting agent, and about 65 to 95weight percent carrier.

D. MICROCAPSULES

Microcapsules are fully enclosed droplets or granules in which theactive materials are enclosed in an inert porous membrane which allowsthe enclosed materials to escape to the surrounding medium at controlledrates.

Encapsulated droplets are typically about 1 to 50 microns in diameter.The enclosed liquid typically constitutes about 50 to 95% of the weightof the capsule, and may contain a small amount of solvent in addition tothe active materials.

Encapsulated granules are characterized by porous membranes sealing theopenings of the granule carrier pores, trapping the liquid containingthe active components inside for controlled release. A typical granulesize ranges from 1 millimeter to 1 centimeter in diameter. Granulesformed by extrusion, agglomeration, or prilling are useful in thepresent invention as well as materials in their naturally occurringform. Examples of such carriers are vermiculite, sintered clay granules,kaolin, attapulgite clay, sawdust, and granular carbon.

Useful encapsulating materials include natural and synthetic rubbers,cellulosic materials, styrene-butadiene copolymers, polyacrylonitriles,polyacrylates, polyesters, polyamides, polyurethanes, and starchxanthates.

E. IN GENERAL

Each of the above formulations can be prepared as a package containingboth the herbicide and the extender together with the other ingredientsof the formulation (diluents, emulsifiers, surfactants, etc.), or as atank mix in which the components are formulated separately and combinedat the grower site. The two formulations in the tank mix can be ofeither the same type or two different types--e.g., the herbicide inmicrocapsule form and the extender as an emulsifiable concentrate. As afurther alternative, the herbicide and extender can be appliedsequentially. This is less preferred, however, since simultaneousapplication generally produces better results.

In general, any conventional method of application can be used. Thelocus of application can be soil, seeds, seedlings, or the actualplants, as well as flooded fields. Soil application is preferred. Dustsand liquid compositions can be applied by the use of powder dusters,boom and hand sprayers, and spray dusters. The compositions can also beapplied from airplanes as dusts and sprays because they are effective invery low dosages. In order to modify or control the growth ofgerminating seeds or emerging seedlings, as a typical example, the dustand liquid compositions are applied to the soil according toconventional methods and are distributed to a depth of at least one-halfinch below the soil surface. The compositions can either be mixed withthe soil particles by discing, dragging, or mixing operations, orsprayed or sprinkled over the surface of the soil. The composition canalso be added to irrigation water so that they will accompany the wateras it penetrates the soil.

The amount of active ingredient required for herbicidal effectivenessdepends upon the nature of the seeds or plants to be controlled and theprevailing conditions. Usually, herbicidal effects are obtained with anapplication rate of about 0.01 to about 50 pounds per acre, preferablyabout 0.1 to about 25. It will be readily apparent to one skilled in theart that compositions exhibiting lower herbicidal activity will requirea higher dosage than more active compounds for the same degree ofcontrol.

What is claimed is:
 1. A method of extending the soil life of athiolcarbamate having the formula ##STR16## in which R¹, R², and R³ areindependently C₂ -C₄ alkyl; which comprises applying to the soilcontaining said thiolcarbamate or to which said thiolcarbamate is to beapplied an effective amount of a 4-phenyl-1,2,3-thiadiazole having theformula ##STR17## in which R⁴ is selected from the group consisting oftrifluoromethyl and ##STR18## in which R⁵ is selected from the groupconsisting of C₁ -C₃ alkyl, phenyl, and phenyl substituted with one ormore members selected from the group consisting of halogen andtrifluoromethyl.
 2. A method of extending the soil life of S-ethylN,N-di-n-propylthiolcarbamate which comprises applying to the soilcontaining said thiolcarbamate or to which said thiolcarbamate is to beapplied an effective amount of a 4-phenyl-1,2,3-thiadiazole having theformula ##STR19## in which R⁴ is selected from the group consisting oftrifluoromethyl and ##STR20## in which R⁵ is selected from the groupconsisting of methyl, chlorophenyl, dichlorophenyl,trifluoromethylphenyl, and chlorotrifluoromethylphenyl.
 3. A methodaccording to claim 2 in which said 4-phenyl-1,2,3-thiadiazole has theformula ##STR21##
 4. A method according to claim 2 in which said4-phenyl-1,2,3-thiadiazole has the formula ##STR22##
 5. A methodaccording to claim 2 in which said 4-phenyl-1,2,3-thiadiazole has theformula ##STR23##
 6. A method according to claim 2 in which said4-phenyl-1,2,3-thiadiazole has the formula ##STR24##
 7. A methodaccording to claim 2 in which the weight ratio of thiolcarbamate to4-phenyl-1,2,3-thiadiazole is from about 1:1 to about 2:1.
 8. Anherbicidal composition of extended soil life comprising an herbicidallyeffective amount of S-ethyl N,N-di-n-propylthiolcarbamate and an amountof a 4-phenyl-1,2,3-thiadiazole sufficient to extend the soil life ofsaid thiolcarbamate wherein said 4-phenyl-1,2,3-thiadiazole has theformula ##STR25##
 9. An herbicidal composition of extended soil lifecomprising an herbicidally effective amount of S-ethylN,N-di-n-propylthiolcarbamate and an amount of a4-phenyl-1,2,3-thiadiazole sufficient to extend the soil life of saidthiolcarbamate wherein said 4-phenyl-1,2,3-thiadiazole has the formula##STR26##
 10. An herbicidal composition of extended soil life comprisingan herbicidally effective amount of S-ethylN,N-di-n-propylthiolcarbamate and an amount of a4-phenyl-1,2,3-thiadiazole sufficient to extend the soil life of saidthiolcarbamate wherein said 4-phenyl-1,2,3-thiadiazole has the formula##STR27##
 11. A method of controlling undesirable vegetation comprisingapplying to the locus where control is desired both an herbicidallyeffective amount of S-ethyl N,N-di-n-propylthiolcarbamate and an amountof a 4-phenyl-1,2,3-thiadiazole sufficient to extend the soil life ofsaid thiolcarbamate wherein said 4-phenyl-1,2,3-thiadiazole has theformula ##STR28##